While almost everyone has experienced an earthquake of moderate strength, which rattles cups and saucers, very few people have been subjected to an earthquake comparable to the great San Francisco earthquake which occurred around the turn of the century and caused considerable damage. Having not experienced a large earthquake, most people would be interested in experiencing a demonstration which would resemble as closely as possible the real quake without the attendant danger. Applicants have succeeded in inventing a vibrating platform machine which will provide the trembling earth sensation required for such an earthquake simulation. When video and audio presentations accompany this trembling earth sensation, and the demonstration is conducted in a closed booth, a very realistic effect is created for the person in the booth.
It can be appreciated that there are several major problems that applicants had to overcome with their design that are inherent in such a machine.
Perhaps the hardest problem to solve is eliminating the transmission of vibration from the earthquake machine to the containing building. Any building which is subject to repeated vibration over an extended period of time will develop structural problems which it might not otherwise develop. If a design depends on anchoring the machine to bedrock to overcome this problem, the installation becomes very expensive and for all practical purposes is limited to ground floor installations. Applicants' design requires no special installation or mounting and is not restricted to use on the ground floor. Applicants' apparatus provides a vibrating surface while transmitting only a greatly attenuated vibration through its frame to the floor.
Another problem inherent in an earthquake machine is the danger of injuring people by providing too "hard" a shock, during a demonstration, which would possibly damage cartilage of the ankle or knee or injure the spine. A "hard" shock is produced in designs which too rapidly accelerate the person experiencing the vibrations produced. Applicants' design prevents against this by producing "soft" shocks.
Injury could also be caused by some designs if the control fails, causing the main driving means to drive the vibrating platform beyond its normal amplitude. This could seriously injure anyone experiencing the demonstration as well as possibly damaging the machine. Applicants' design avoids this possibility.